Whoops! The previous posting linked to the C.C. Silver & Gold page having 99.9% pure silver wire, not the necessary 99.99% pure silver wire you want. Here's my tweet...Silver Shadow, the recycled runty Kansas barn cat, is perched on my shoulder, approving of all things silver.
.99% is not 'necessary' as you put it, .9+% is perfectly OK.
.9+% would be the minimum purity one should use in their silver, and the amount of impurities in .9 as compared to .99 are so negligible so as not to be worth worrying about, .99 or purer is good, I agree, but it's not 'necessary'.